Surface acoustic wave induced electron tunneling from an InGaAs/GaAs wetting layer

We report on a stroboscopic technique to probe the dynamic modulation controlled by a surface acoustic wave (SAW) of the photoluminescence (PL) of a wetting layer which is formed during the growth of InGaAs/GaAs quantum dots. A short laser pulse (τ <100 ps) is actively phase locked to the frequency of the SAW and the relative phase between laser excitation and SAW can be precisely controlled. Thus, we are able to map one complete cycle of the SAW and study the PL quenching and its modulation in the time domain. For low SAW powers the observed modulation with the fundamental period of the SAW arises from different mobilities of electrons and holes. This imbalance leads to different ionization efficiencies in the type-II band gap modulation induced by the SAW. At high SAW power levels, the modulation period doubles which can be readily explained by SAW induced tunneling induced by the vertical piezoelectric field component.